This invention relates to dynamoelectric machines and more particularly to permanent magnet rotors for use in such machines.
High power density, lightweight generators and motors have been used for many years in military and commercial aircraft. A requirement for lightweight units has resulted in the design of higher speed motors and generators to maximize the power to weight ratios of the units. Recent advances in permanent magnet materials, such as the development of ferrite and rare earth compounds, have allowed designers to further increase the power density of rotating airborne electrical equipment.
The use of permanent magnet materials in high speed rotating electrical equipment poses a number of problems with respect to material support and the definition of magnetic flux paths which have hindered the application of these materials to very high speed machines. U.S. Pat. No. 4,354,126, issued Oct. 12, 1982, to W. W. Yates discloses a permanent magnet rotor which illustrates the current state of the art. In the disclosed rotor, a plurality of permanent magnets are embedded in rotor slots and are arranged in combination with a plurality of magnetic pole pieces to form a series of magnetic poles on the surface of the rotor. These magnetic poles force flux through several paths within the machine. The path which links the stator windings and produces useful torque is known as the main flux path. Other paths which do not link the stator winding circuit produce no torque and are commonly called leakage flux paths.
A primary design consideration in permanent magnet machines which utilize ferrite and rare earth magnet compounds is the minimization of leakage flux paths. Several permanent magnet rotor designs have been proposed which required the bonding of magnetic and nonmagnetic materials in a high speed rotor configuration. This type of bonding is difficult to implement in the rotor manufacturing process.